The invention relates to a method and a regulating system for damping the torque oscillations of the drive train of an electrically driven road vehicle.
An important problem associated with the drive trains of electrically driven road vehicles is the oscillations caused by the elasticity and gear play in the mechanical connections. The oscillations have a material-fatiguing effect on the vehicle components and reduce passenger comfort.
The fundamental task of the drive system is to transmit the torque requested by the driver to the wheels. Because of the elasticity and play of the drive train components, unless suitable suppression is carried out resonant phenomena always occur as the natural damping of an electric drive is very low.
Various methods for damping the oscillations are known from the prior art. U.S. Pat. Nos. 5,821,720 and 5,994,859 disclose, for example, simple damping methods which use only motor measurement variables as input variables. As a result, the damping is inadequate and depends, undesirably, on the operating point.
Furthermore, in Marcus Menne, Dissertation, RWTH Aachen, 2001, Wissenschaftsverlag Mainz, a method for damping using further parameters as input variables is disclosed which likewise depends on the operating point.
The invention is thus based on an object of developing a method for damping the torque oscillations of the drive train of an electrically driven road vehicle which ensures adequate damping and has a travel characteristic which is significantly better than the prior art. In addition, a regulating system for carrying out the method is to be developed.
The first-mentioned object is achieved by a method of the present invention in which the torque (or an estimated value) and the rotational speeds of the electric motor which drives the vehicle and of one or more wheels of the vehicle are detected as input variables. In addition, an observer estimates, from the input variables, the torque which is transmitted to the wheels by the gear mechanism. Further, a regulating block which is connected downstream of the observer determines a compensation torque from the estimated torque, and the compensation torque is added to the setpoint torque of the electric motor. All of this results in a regulating circuit.
With the present method, the drive train oscillations are effectively damped. The method functions at all relevant operating points. It leads to a significantly better travel characteristic which has the effect of improving passenger comfort. The achieved damping of the torque oscillations places significantly less mechanical loading on the drive train. As a result, the material fatigue of the drive train is significantly reduced, and its service life prolonged.
In particular, when the torque transmitted to the wheels by the gear mechanism drops below a predefined threshold value, the regulating system may be switched off after a predefined time delay, and not switched on again until the threshold value is exceeded. The regulating system is preferably switched off when the vehicle is stationary. A logic unit which switches off the regulator when the torque is very small or none is added. In this configuration, no compensation torque is generated. If the requested torque is of the same order of magnitude as the noise level, it is more advantageous not to add a compensation torque to the setpoint torque of the electric motor.
In a further refinement of the invention, the regulating system is active only if the values for the compensation torque are in a predefined interval. As a result, functional errors in extremely unusual travel situations are avoided. Sensor errors or failures can thus also be taken into account. Unstable operating methods are completely ruled out by the specified variants.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.